We present time-resolved optical spectroscopy and
photometry, and far-ultraviolet spectroscopy of
HS 0728+6738, a cataclysmic variable discovered in the Hamburg
Quasar Survey. We show that the system is a new eclipsing member of
the SW Sex class of CVs with an orbital period of 3.21 h. We derive an orbital inclination of ~ from the
average eclipse profile, making HS 0728+6738 the highest inclination
SW Sex star known. The optical and far-ultraviolet emission
lines are not or only weakly occulted during the eclipse, indicating
the presence of line-emission sites either far outside the Roche lobe
of the primary or, more likely, above the orbital plane of the binary.
The photometric light curves exhibit fast variability with a period of
~7 min, which might be related to the spin of the white dwarf.

Based
in part on observations obtained at the German-Spanish Astronomical
Center, Calar Alto, operated by the Max-Planck-Institut für
Astronomie, Heidelberg, jointly with the Spanish National Commission
for Astronomy, on observations made with the IAC80 telescope, operated
on the island of Tenerife by the Instituto de Astrofísica de
Canarias (IAC) at the Spanish Observatorio del Teide, on observations made at the Wendelstein Observatory, operated by the Universitäts-Sternwarte München, and on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the
Association of Universities for Research in Astronomy, Inc., under
NASA contract NAS 5-26555.

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